1. Field of the Invention
The present invention relates to an optical information recording medium, an optical information recording apparatus and an optical information recording method which may be applied to a magnetooptical disc (MO), a compact disc (CD, CD-ROM (compact disc-read-only memory)), a digital video disk (DVD) and a recording method and a recording apparatus of these discs, for example.
2. Description of the Related Art
Heretofore, a recording apparatus for a compact disc made of this kind of optical information recording medium processes recording data and then EFM (eight-to-fourteen modulation)-modulates the processed data to form a pit string having periods 3T to 11T with respect to a fundamental period T, thereby resulting in audio data or the like being recorded.
Corresponding thereto, a compact disc player receives a returned light of a laser beam reflected on the surface of a compact disc surface after having irradiated the laser beam on the surface of the compact disc and obtains a reproduced signal the signal level of which changes in response to a quantity of light of this returned light. Then, the compact disc player generates a binary signal by binarizing this reproduced signal with a predetermined slice level. Further, the compact disc player generates a reproducing clock by driving a PLL (phase-locked loop) circuit with this binary signal, and sequentially latches the binary signal by this reproducing clock, thereby resulting in reproduced data of the periods 3T to 11T corresponding to the pit string formed on the compact disc being generated.
The compact disc player decodes the reproduced data thus generated by the data processing corresponding to the data processing during the recording mode to reproduce audio data or the like recorded on the compact disc.
Recently, it has becomes customary that such compact disc are recorded at a high density and reproduced at a high transfer rate. In order to realize high-density recording and high-transfer rate reproduction, there has heretofore been used a land groove recording format in which pits are formed on both the lands and the grooves of the disc. According to the land groove recording format, a track pitch may be reduced, thereby making it possible to increase a disc recording capacity.
Also, according to the land groove recording format, when address information is recorded on the disc, the same address information is recorded on an adjacent land and a groove and one of two laser beams is wobbled in such a manner that data, that was recorded at the same address information, may be read out. A reproducing apparatus having a high transfer rate reproduces data at a high speed by rotating a compact disc, for example, at revolutions higher than 8 times a predetermined revolution number. Such high-transfer rate reproducing apparatus is able to reproduce data of the same amount in quite a short period of time as compared with the normal one time.
As shown in FIG. 1, when a disc is manufactured, the groove is cut by using spots 201, 202 of two laser beams. When one of the two laser beam is wobbled, a distance between the two laser beams and the laser powers of the two laser beams have to be adjusted with high accuracy in such a manner that the spot 202 of the wobbled laser beams may not invade the spot 201 of the other laser beam which is not wobbled. To this end, the sizes of the laser beams for use in cutting should be calculated from the distance between the two laser beams relative to the determined groove width. However, as shown in FIG. 2, two laser beams 205 (LA0, LB0) have beam intensity distributions (SA0, SB0, added distribution S0), and hence widths (WA0 to WB0) of the groove 203 are determined by a combination of the beam intensity distributions and disc exposure conditions such as an exposure threshold 206 (TH) in a disc cutting direction 204. Even though the adjusted beam distance and light intensity are calculated by the above-mentioned factors, when address information is recorded on the groove by wobbling one of the two laser beams, the light intensity of one laser beam is added to the other laser beam, which is not wobbled, by the wobbled amount so that the groove, which should not be modulated by the other laser beam, is modulated by the influence of the offset. As a consequence, upon reproduction, the offset signal is superimposed upon the reproduced signal. There is then the disadvantage that address information cannot be reproduced at a high accuracy.